1. Field of The Invention
The present invention relates to semi-automatic mechanical change gear transmissions. In particular, the present invention relates to an improved semi-automatic mechanical change gear transmission system having means to sense manual selection of a particular gear ratio, means to sense and/or calculate the rotational speed of the jaw clutch members associated with the selected gear ratio, a power synchronization device for selectively accelerating and/or decelerating the rotational speed of input shaft driven transmission members, preferably independent of the rotational speed of the prime mover, and a device to inhibit movement of the shift rails until synchronization of the clutch members of the selected jaw clutch is sensed.
2. Description of the Prior Art
Manually shifted, non-synchronized, nonblocked, mechanical, constant mesh, change gear transmissions, usually for driving a land vehicle from a prime mover such as an Otto cycle or diesel engine, are well known in the prior art. Examples of such transmissions may be seen by reference to U.S. Pat. Nos. 3,105,395; 3,138,965; 3,283,613 and 3,611,823, the disclosures of which are hereby incorporated by reference. This type of transmission utilizes selectively engageable positive or jaw clutches which are usually moved axially into and out of engagement by shift forks carried by shift bars or rails. Positive clutches of this type are relatively compact and inexpensive as compared to friction clutches, synchronized clutches and/or blocked clutches and are very reliable if utilized in connection with some type of synchronizing means.
Conventional, individually sychronized and/or blocked positive clutch structures are well known in the prior art as may be seen by reference to U.S. Pat. Nos. 3,221,851; 3,929,029; 4,307,624; 4,497,396; 3,799,002; 4,428,469 and 4,132,122, the disclosures of which are hereby incorporated by reference. Conventional individual synchronizing devices, while providing easy shifting of gears in a transmission, require a relatively large space in the transmission housing and, due to the relatively limited space available within a transmission housing are of a relatively limited capacity and/or life. This is especially true for transmissions utilized with heavy duty vehicles wherein the torque transfer capacities and inertias involved are relatively great. Individual blocked positive clutch assemblies, while providing relatively easy shifting of the transmission, do require a certain degree of skill to cause a crossing of synchronization and further are more complicated and space consuming than a conventional nonsynchronized nonblocked jaw clutch assembly.
Synchronizing of conventional nonsynchronized, nonblocked jaw clutch assemblies by operator manipulation of engine speed, usually involving the use of an input shaft or engine brake and "double clutching", highly efficient, well known and widely used transmission shifting method. However, such manual synchronizing of mechanical transmissions requires a high degree of operator skill, effort and attention and thus may not be suitable for situations where unskilled operators may be utilized and/or the operator'attention is best directed to other matters such as to vehicle operation in a highly congested traffic situation.
Automatic mechanical transmission systems wherein electronic central processing units are utilized to automatically cause synchronization of positive jaw clutches by automatic manipulation of engine speed and the vehicle master clutch are also known in the prior art as may be seen by reference to U.S. Pat. No. 4,361,060, the disclosure of which is hereby incorporated by reference. Such control systems are best suited for a fully automatic transmission system and not for a semi-automatic transmission system, require rather complicated engine and master clutch controls and further, when synchronizing the jaw clutches for a downshift, are limited by the engine governed speed, acceleration and response times as to speed, acceleration and response time of the transmission input shaft driven jaw clutch members.
Semi-automatic mechanical transmissions utilizing power synchronizing devices, i.e. devices for accelerating and decelerating the rotational speed of transmission elements such as shafts, gears and jaw clutch members rotatably driven by the input shaft of a nonconventionally synchronized mechanical change gear transmission independently of the speed of the drive engine are known in the prior art. Examples of such transmissions and power synchronizing devices may be seen by reference to U.S. Pat. Nos. 3,478,851; 3,736,806 and 4,023,443, the disclosures of which are hereby incorporated by reference. The known prior art transmissions utilizing such devices have required an auxiliary external power source, have required major modification of the host transmission and/or have been limited by the transmission gear ratios as to acceleration and/or maximum rotational speed of the input shaft driven transmission elements for purposes of synchronizing same with the main shaft or output shaft during a downshift.
It has proven difficult to package a downshift power synchronizing device and a means to prevent axial movement of the shift rails until synchronous rotation of the selected jaw clutch members is sensed into a standard manual constant mesh nonsynchronized transmission without making major modifications to the host transmission. The reason for this is that standard transmissions, especially for heavy duty trucks, tend to be highly optimized packages with component densities that are very high in order for the transmission to fit between the vehicle frame rails or within the compartmental constraints of a vehicle and still allow for standard add-on features such as power take-offs, shift linkages and the like. No commercially available production semi-automatic mechanical transmission utilizing a power synchronizing device and shift rail blocking device is known to exist at this time.